1. Field of the Invention
The present invention relates to the controlling of pressure in a fluid system. More particularly, the present invention relates to a method of and apparatus for establishing and maintaining a predetermined level of pressure within at least one processing chamber that forms part of a closed atmosphere.
2. Description of the Related Art
In general, the manufacturing of high-tech products, including semiconductor devices, requires establishing precise conditions in a production environment to achieve high yields. These conditions include pressure, temperature, environmental purity and the like. In such a production environment, pressure is regarded as a key factor in preventing the influx of external contaminants as well as a parameter necessary for facilitating certain processes. An example of a production environment in which a certain level of pressure must be established and maintained will be described with reference to prior art semiconductor device manufacturing and processing facilities.
FIG. 1 illustrates a prior art multi-chamber semiconductor device manufacturing and processing facility. In this facility 10, loadlock chambers 12a, 12b are coupled by doors D, at one side of the facility, for selective communication with a production line. Initially, a cassette C filled with a plurality of wafers W is inserted from the production line into a respective one of the loadlock chambers 12a, 12b. The environment inside the loadlock chamber 12a, 12b is then isolated from the production line when the door D is closed. Subsequently, a vacuum is created within the loadlock chamber 12a, 12b. 
The facility 10 also includes a transfer chamber 14 positioned at one side of the loadlock chambers 12a, 12b. The transfer chamber is disposed in-line with the loadlock chambers 12a, 12b and is placed in selective communication therewith via doors D′. The inside of the transfer chamber 14 is generally kept at a predetermined negative pressure, which will hereinafter be referred to as vacuum pressure. In addition, a robot 16 is installed at a predetermined position within the transfer chamber 14. The robot 16 is configured to fixedly support individual wafers and is programmed to transfer the wafers to various positions within the facility 10.
Processing chambers 18a, 18b for processing the wafers and auxiliary chambers 20a, 20b, 20c, 20d for performing pre- and post-processing steps are installed at the other side of the transfer chamber 14. The processing chambers 18a, 18b and the auxiliary chambers 20a, 20b, 20c, 20d selectively communicate with the transfer chamber 14 via respective doors D′. Like the transfer chamber 14, the insides of the processing chambers 18a, 18b and auxiliary chambers 20a, 20b, 20c, 20d are all kept at a predetermined vacuum pressure.
In this type of facility, one purpose of the loadlock chambers 12a, 12b is to provide a transition for the wafers—from the room pressure state of the processing line to the vacuum pressure required for the processing of the wafers. Another purpose of the loadlock chambers 12a, 12b is to prevent particles from the production line from invading the downstream chambers when the wafers are introduced into the processing facility 10.
The time that it takes to change the pressure state in a loadlock chamber 12a, 12b, from room pressure to the required vacuum pressure state and vice versa, is proportional to the size of the loadlock chamber 12a, 12b. Therefore, any unnecessary space within the loadlock chambers 12a, 12b must be minimized in an effort to reduce the overall processing time.
Moreover, the pressure states within any of the chambers 12a, 12b, 14, 18a, 18b, 20a, 20b, 20c, 20d must be maintained when the doors D′ associated therewith are simultaneously open while the wafers W are being transferred therebetween. Otherwise, the gas within these chambers would flow out due to a pressure difference between the chambers. If the gas were to flow from one chamber to another, the gas might entrain particles, whereby the wafers W or the processing facility 10 could become contaminated. Also, the flow of gas might give rise to an eddy phenomenon which could, in turn, bring about a change in other processing conditions such as temperature, the supply of processing gas, pressure and the like. In these cases, the changes in the processing conditions could lead to processing failures.
Conventional pressure control apparatus 60 for balancing the pressure between first and second mutually communicating object chambers is shown in FIG. 4. Pressure sensors 66a, 66b are installed on respective sides of the first and second object chambers 62a, 62b, for detecting the internal pressure levels of the first and second object chambers 62a, 62b, respectively, and separately transmitting the signals indicative of the pressure levels to a controller 64.
Also, pressure supply systems 68a, 68b are coupled to other sides of the first and second object chambers 62a, 62b for supplying a predetermined level of pressure into the object chambers 62a, 62b according to the control signals transmitted from the controller 64. The pressure supply systems 68a, 68b comprise a vacuum pump 70 connected to the object chambers 62a, 62b by vacuum lines Va, Vb, respectively, a gas supply device 72 connected to the object chambers 62a, 62b by gas supply pipes Sa, Sb, respectively, and valves 74a, 74b, 74c, 74d disposed in the vacuum lines Va, Vb and the gas supply pipes Sa, Sb for selectively shutting down the flow of gas therethrough.
The pressure control system 60 attempts to establish an identical level of pressure between the first and second object chambers 62a, 62b as follows. First, the controller 64 respectively checks the internal pressures of the first and second chambers 62a, 62b with the pressure sensors 66a, 66b. If there is a difference in pressure between the first and second object chambers 62a, 62b, the valves 74a, 74b, 74c, 74d in the vacuum lines Va, Vb and gas supply lines Sa, Sb are selectively controlled and opened to supply vacuum pressure or purge gas, thereby adjusting the internal pressure levels of the first and second object chambers 62a, 62b. Then, when the pressure levels of the first and second object chambers 62a, 62b reach the required levels, the controller 64 the valves 74a, 74b, 74c, 74d in the vacuum lines Va, Vb or gas supply pipes Sa, Sb. At the same time, the controller 64 controls the operations of the vacuum pump 70 and the gas supply device 72.
The pressure within the first and second object chambers 62a, 62b is controlled by supplying vacuum pressure or purge gas based on signals generated by the pressure sensors 66a, 66b until the desired internal pressures of the first and second object chambers 62a, 62b are established. However, the detected levels of pressure are not always accurate while the pressure levels are being adjusted, and it is difficult to effect the delicate feedback control required in providing vacuum pressure or purge gas while the pressure levels are being adjusted.
Furthermore, if the internal pressure level of the object chambers becomes exceeds the desired vacuum pressure or positive pressure, additional purge gas or vacuum pressure must be supplied to the respective object chambers, thereby delaying the processing of the wafers. Accordingly, it is important to form a very precise internal pressure within the object chambers from the start. Therefore, the pressure sensors 66a, 66b must be able to detect the static pressure level of the object chambers.
FIG. 2 illustrates a bell-shaped chamber of a semiconductor device manufacturing and processing facility that simultaneous processes a plurality of wafers. The processing facility 30 includes a loadlock chamber 32 for loading wafers W and a processing chamber 34 disposed over the loadlock chamber 32 for processing the wafers W.
A boat 38 containing a plurality of wafers W is raised from the loadlock chamber 32 to introduce the wafers W into the processing chamber 34. At this time, a block plate 36 seals off the atmosphere of the upper processing chamber 34 from that within the loadlock chamber 32. Then, the wafers W are processed by processing gas at a predetermined vacuum pressure atmosphere and at a certain temperature.
When the processing of the wafers W is completed, the boat 38 loaded with the wafers W is lowered back down into the loadlock chamber 32 while the block plate 36 allows the atmospheres within the processing chamber 34 and the loadlock chamber 32 to communicate.
In this type of facility 30, the atmospheres within the processing chamber 34 and the loadlock chamber 32 become different in terms of pressure and temperature, thereby leading to a natural flow of gases when the block plate 36 opens the processing chamber 34. Even when a balanced pressure state is formed between the processing chamber 34 and the loadlock chamber 32 before the processing chamber 34 is opened by the block plate 36, the relative size of the effective spaces within the processing chamber 34 and the loadlock chamber 32 continuously change by as much as the volume of the block plate 36 and the boat 38. As a result, a pressure differential is produced, thereby causing gas to flow between the loadlock chamber 32 and the processing chamber 34. In this case, particles within the loadlock chamber 32 are introduced into the processing chamber 34, resulting in the contamination of the wafers W and the processing chamber 32.
Also, the various gases induced into the processing chamber 34 are at a relatively low temperature. Accordingly, the wafers W at the bottom of the boat 38 cool more rapidly than those at the top of the boat 38. This condition produces differences in the processed states of the wafers W and leads to a sudden crystallization of the gas remaining within the processing chamber 34. As a result, particles are created and the processed wafers W are not uniform.
Therefore, in order to solve the aforementioned problems, efforts should be made to achieve a pressure balance between the processing chamber 34 and the loadlock chamber 32 and to minimize a change in pressure and temperature caused by the volumetric fluctuations due to the movement of the block plate 36 and the boat 38.
Conventional pressure control apparatus aimed at solving the problems of the prior art in the manner described above is shown in FIG. 3. The apparatus 40 includes an object chamber 42, a controller 44, a pressure sensor 46 for detecting the pressure within the object chamber 42 and transmitting a signal indicative of the detected pressure to the controller 44, and a pressure supply system 48.
The pressure supply system 48 is installed at one side of the object chamber 42 for creating a predetermined level of pressure within the object chamber 42 according to a control signal input thereto from the controller 44. The pressure supply system 48 includes a gas supply device 52 connected to the object chamber 42 by a gas supply pipe S, a vacuum pump 50 connected to the object chamber 42 by a vacuum line V, and valves 54a, 54b for selectively stopping the flow of gases through the gas supply pipe S and vacuum line V.
Next, the steps of establishing a predetermined vacuum pressure within the object chamber 42 will be described. First, the controller 44 drives the vacuum pump 50 with the valve 54b open to create a predetermined vacuum pressure within the object chamber 42. In the course of the operation, the controller 44 continuously monitors the internal pressure of the object chamber 42 with the pressure sensor 46. When the internal pressure of the object chamber 42 approaches the desired level, the controller 44 controls the degree of opening of the valve 54b on the vacuum line V. Then, when the internal pressure state of the object chamber 42 reaches the required level of pressure, the controller 44 closes the valve 54b and at the same time shuts down the operation of the vacuum pump 50.
On the other hand, a room pressure atmosphere is established within the object chamber 42 as follows. The controller 44 opens the valve 54a of the gas supply pipe S and drives the gas supply part 52 to supply a predetermined purge gas into the object chamber 42. The internal pressure of the object chamber 42 is detected by the pressure sensor 46 and a signal indicative of the pressure is transmitted to the controller 44. The controller 44 controls the valve 54a and the gas supply part 52 until the internal pressure of the object chamber 42 reaches room pressure.
However, it is difficult to accurately establish a desired level of pressure by controlling the degree of opening of the valves 54a, 54b and the operations of the vacuum pump 50 and gas supply part 52. In particular, the pressure in the object chamber 42 becomes unstable while fluid is flowing thereinto/therefrom in the course of providing the chamber 42 with vacuum pressure or purge gas. Accordingly, the pressure detected by the pressure sensor 46 is unreliable, and it is difficult to precisely control the supply of vacuum pressure or purge gas.
Moreover, the pressure in the object chamber 42 has a direct effect on the processing that occurs in the chamber. Therefore, an important aspect of the processing operation is to form an extremely precise pressure state in the object chamber 42. If the internal pressure level of the object chamber 42 becomes higher than the desired vacuum pressure or a predetermined high pressure, purge gas or vacuum pressure must be provided immediately. Thus, the pressure sensor 46 must detect the static pressure state of the object chamber 42, so that it is possible to keep the pressure level of the object chamber 42 precise, that is, neither lower nor higher than the required pressure level.